[FFmpeg-devel] [PATCH] Speed up wtv index creation

[Peter Ross]

On Fri, Jan 29, 2016 at 09:36:30PM +0000, popcorn mix wrote:
> The index creation is O(N^2) with number of entries (typically thousands).
> On a Raspberry Pi this can take more than 60 seconds to execute for a recording of a few hours.
>     
> By replacing with an O(N) loop, this takes virtually zero time
> 
> This patch has been in all Pi builds of Kodi for the last couple of years,
> so it is quite widely tested. No change in FATE output.
>
> From 4bad5dbd752e96a6dfcb7e46aff1d64996d08ed1 Mon Sep 17 00:00:00 2001
> From: popcornmix <popcornmix at gmail.com>
> Date: Fri, 29 Jan 2016 20:27:00 +0000
> Subject: [PATCH] wtv: Speed up wtv index creation
> 
> The index creation is O(N^2) with number of entries (typically thousands).
> On a Pi this can take more than 60 seconds to execute for a recording of a few hours.
> 
> By replacing with an O(N) loop, this takes virtually zero time
> ---
>  libavformat/wtvdec.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
> index e8f6196..b329b7c 100644
> --- a/libavformat/wtvdec.c
> +++ b/libavformat/wtvdec.c
> @@ -1028,21 +1028,23 @@ static int read_header(AVFormatContext *s)
>                  pb = wtvfile_open(s, root, root_size, ff_timeline_table_0_entries_Events_le16);
>                  if (pb) {
>                      int i;
> +                    AVIndexEntry *e = wtv->index_entries;
> +                    AVIndexEntry *e_end = wtv->index_entries + wtv->nb_index_entries - 1;
> +                    uint64_t last_position = 0;
>                      while (1) {
>                          uint64_t frame_nb = avio_rl64(pb);
>                          uint64_t position = avio_rl64(pb);
> +                        while (frame_nb > e->size && e <= e_end) {
> +                           e->pos = last_position;
> +                           e++;

^^^ this indent isn't aligned.

otherwise, great stuff. your implementation is solid.

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
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